1. Field of the Invention
The present invention relates to an electrostatic ink jet recording head which accomplishes recording to a recording medium by using charged particulate materials in ink, and more particularly to an electrostatic ink jet recording apparatus which prevents precipitation of charged particulate material in ink.
2. Description of the Prior Art
An electrostatic ink jet recording apparatus according to the prior art, as disclosed in PCT Publication number WO 93/11866, has an electrostatic ink jet recording head and a counter electrode arranged behind recording paper. The counter electrode is provided for generating an electric field between the recording paper and the ink jet recording head. The ink jet recording head has an ink chamber for temporarily storing ink liquid supplied from an ink tank or the like. An ejection electrode is formed at an end of the ink chamber and driven when the ink is ejected. The tip of that ejection electrode is opposite to the counter electrode. The ink liquid in the ink chamber is fed by its own surface tension to the tip of the ejection electrode, where an ink meniscus is thereby formed.
The ink liquid used with that ink jet recording head contains charged particulate material for coloring. While the charged particulate material is electrified in a positive polarity by a Zeta potential, the ink liquid maintains electric neutrality when no voltage is fed to the ejection electrode. The polarity of the Zeta potential is determined by the characteristic of the charge particulate material.
When a voltage of the positive polarity is fed to the ejection electrode, the positive potential of the ink liquid is enhanced. The charged particulate material is caused by an electric field working between the ejection electrode and the counter electrode to shift in the ink liquid toward the tip of the ejection electrode. The charge particulate material having reached the tip of the ejection electrode is strongly drawn toward the counter electrode by the electric field working between the tip of the ejection electrode and the counter electrode. When the Coulmob force between the charge particulate material at the tip of the ejection electrode and the counter electrode substantially surpasses the surface tension of the ink liquid, an agglomeration of the charge particulate material accompanied by a small quantity of liquid flies from the tip position of the ejection electrode toward the counter electrode, and adhere to the surface of the recording medium. As the agglomeration of the charge particulate material is caused by the application of a voltage to the ejection electrode to successively fly from the tip of the ejection electrode, printing is accomplished.
However, the charge particulate material of the ink liquid used in the electrostatic ink jet recording head is readily precipitated by gravity, and therefore does not distribute evenly in the ink chamber. As a consequence, charge particulates are not steadily supplied to the tip of the ejection electrode, and the quantity of the charge particulate material in the agglomeration flying from the ink ejecting position is inconstant. Accordingly, there is the problem of difficulty to accomplish steady printing.
Furthermore, when the ink liquid in the ink chamber is to be shifted toward the tip of the ejection electrode only by the ejection electrode and the counter electrode, precipitation of the charge particulate material extends the shifting time, making it difficult to achieve high-speed printing.